MobiCS: MobiCS: An Environment for Prototyping An Environment for Prototyping

and Simulating Distributed and Simulating Distributed Protocols for Mobile NetworksProtocols for Mobile Networks

Ricardo C.A. da Rocha (IME/USP)Ricardo C.A. da Rocha (IME/USP)

rcarocha@ime.usp.brrcarocha@ime.usp.br

Markus Endler (PUC-Rio)Markus Endler (PUC-Rio)

endler@inf.puc-rio.brendler@inf.puc-rio.br

OutlineOutline

Motivation and Related WorksMotivation and Related Works System Model and Reference ArchitectureSystem Model and Reference Architecture MobiCS OverviewMobiCS Overview Deterministic simulationDeterministic simulation Stochastic simulationStochastic simulation Example Example ConclusionsConclusions

Motivation Motivation

Characteristics of Mobile Computing Characteristics of Mobile Computing EnvironmentsEnvironmentsDynamic Network TopologyDynamic Network Topology Energy is scarce resource Energy is scarce resource Mobile Mobile

Host may enter doze mode or be turned offHost may enter doze mode or be turned off Wireless communication Wireless communication

unreliable connectivity (e.g. intermittent periods of disconnection)

QoS parameters change very fast lower throughput

Motivation Motivation

Distributed Protocols for Mobile Computing Distributed Protocols for Mobile Computing should...should... handle variable number of interacting nodes handle variable number of interacting nodes make efficient use of wireless communicationmake efficient use of wireless communication consider non-availability consider non-availability failure failure maintain consistent distributed state despite maintain consistent distributed state despite

disconnections disconnections be correct and efficient for any number of hosts be correct and efficient for any number of hosts

(scalability) and mobility pattern (mobility (scalability) and mobility pattern (mobility robustness)robustness)

FactFact: Evaluating the protocol´s correctness and : Evaluating the protocol´s correctness and efficiency are difficult tasksefficiency are difficult tasks

MotivationMotivation Our goal:Our goal:

Build a tool for rapid prototyping and evaluation of Build a tool for rapid prototyping and evaluation of distributed protocols (e.g. multicast, reliable message distributed protocols (e.g. multicast, reliable message delivery, notification protocols) delivery, notification protocols)

Approach:Approach: Protocol evaluation (correctness & Protocol evaluation (correctness & efficiency) through simulation.efficiency) through simulation.

The tool should support:The tool should support:definition of appropriate abstractions for programming definition of appropriate abstractions for programming

the protocol (e.g. message, request-reply, transaction)the protocol (e.g. message, request-reply, transaction)design of network elements with arbitrarydesign of network elements with arbitrary behaviors.behaviors.programming of appropriate simulation models, programming of appropriate simulation models,

specially specially mobility modelsmobility models..

Other Simulators Other Simulators

Protocol developer has also to deal with Protocol developer has also to deal with low-level details.low-level details.

Form of simulation (e.g. parallel) is not Form of simulation (e.g. parallel) is not fully transparent.fully transparent.

Limited extensibility.Limited extensibility. Lack of Lack of integrated supportintegrated support for protocol for protocol

validation and testing.validation and testing. Limited programmabilty of mobility Limited programmabilty of mobility

models.models.

Common LimitationsCommon Limitations

System Model for Protocols in System Model for Protocols in Mobile ComputingMobile Computing

We assume a We assume a structured mobile networkstructured mobile network composed of composed of Mobile Hosts (MHs), Mobility Support Stations (MSSs)Mobile Hosts (MHs), Mobility Support Stations (MSSs)

We adopt the We adopt the Indirect ModelIndirect Model [Badrinath94], where all [Badrinath94], where all communications are split into a communications are split into a wiredwired and a and a wireless partwireless part

Basic unit of interaction in a protocol Basic unit of interaction in a protocol messagemessage If mobile host is reachable, wireless message is delivered. If mobile host is reachable, wireless message is delivered.

But MH may be disconnected or migrating.But MH may be disconnected or migrating. QoS of the wireless connection is modeled as its effective QoS of the wireless connection is modeled as its effective

transmission rate.transmission rate. Hand-Off is initiated by the MHHand-Off is initiated by the MH At any time, every MH is associated with exactly one MSSAt any time, every MH is associated with exactly one MSS

Reference Architecture for Reference Architecture for SimulationSimulation

Application makes service Application makes service requests (user or requests (user or automatically generated)automatically generated)

Distributed Protocols are Distributed Protocols are programmed and tested programmed and tested

Network Elements implement Network Elements implement HWHW and and basic SWbasic SW functionality (OS, low-level functionality (OS, low-level Netw. Protocols) Netw. Protocols)

Simulation Engine:Simulation Engine: schedules event processing orderschedules event processing order may implement several may implement several

simulation modes. simulation modes.

Simulation Simulation EngineEngine

Network ElementsNetwork Elements

ApplicationApplication

Distributed Distributed ProtocolsProtocols

MobiCSMobiCSMobiMobile CComputing SSimulator MobiCSMobiCS is a java class library implementing the is a java class library implementing the

Reference ArchitectureReference Architecture Main Advantages:Main Advantages:

Single tool Single tool for prototyping, validating and analysing for prototyping, validating and analysing distributed protocols.distributed protocols.

A generic Simulation Engine API offers completeA generic Simulation Engine API offers complete transparency of simulation modestransparency of simulation modes..

ProgrammableProgrammable and and customizable simulation modelscustomizable simulation models (e.g. mobility, connectivity, etc.)(e.g. mobility, connectivity, etc.)

Supports the Supports the creation of abstractionscreation of abstractions for protocol for protocol implementation.implementation.

Comes with a Comes with a deterministicdeterministic and a and a stochasticstochastic simulation simulation modemode (others may be added). (others may be added).

MobiCS:MobiCS:Protocol Programming Protocol Programming

Object-oriented protocol design Object-oriented protocol design Protocols are composed of Protocols are composed of micro-protocolsmicro-protocols, which , which

interact through interact through eventsevents (mainly, messages and (mainly, messages and timers)timers)

Main Protocol Components:Main Protocol Components:

Micro-protocols are Java interfaces whose Micro-protocols are Java interfaces whose methods are handlers for the events.methods are handlers for the events.

Protocol

WiredWired WirelessWireless HandoffHandoff

MobiCS:MobiCS:Deterministic Simulation Deterministic Simulation Used for debugging/testing the correctness of the Used for debugging/testing the correctness of the

protocol.protocol. A user creates a simulation A user creates a simulation scriptscript, which is executed by , which is executed by

the simulator. the simulator. This script describes a specific scenario (i.e. pattern of This script describes a specific scenario (i.e. pattern of

protocol-external eventsprotocol-external events) ) Events may be application requests, MH migrations, Events may be application requests, MH migrations,

MH disconnections, etc.MH disconnections, etc. Global synchronization points Global synchronization points end_step()end_step() in the script in the script

define the causal order relationship among the events.define the causal order relationship among the events. Message acceptance can be toggled on/off to simulate Message acceptance can be toggled on/off to simulate

message transmission delays: message transmission delays: Accept(msgTypeAccept(msgType)) and and AcceptTurnOn(bool)AcceptTurnOn(bool)..

MobiCS:MobiCS:Deterministic Simulation Deterministic Simulation

Example:Example:

The simulation executes in steps (i.e. there is no notion The simulation executes in steps (i.e. there is no notion of simulated time)of simulated time)

Scripts should reflect Scripts should reflect critical situationscritical situations in which the in which the protocol behaviour is to be tested.protocol behaviour is to be tested.

Since only a minimal fraction of all possible situations Since only a minimal fraction of all possible situations can be described, this method gives can be described, this method gives no guarantee of the no guarantee of the protocol´s correctness protocol´s correctness testing testing

Mh1.moveTo(cell1); // Mh1 at cell of Mss3Mh1.send(new Req);Mss3.accept(Req);end_step();

Mh2.unavailable();

Mh1.moveTo(cell1); // Mh1 at cell of Mss3Mh1.send(new Req);Mss3.accept(Req);end_step();

Mh2.unavailable();

MobiCS:MobiCS:Deterministic Simulation Deterministic Simulation

server

Home agent (ha)

MSSo

MSSn

mh

req

req

res

res

res

C

ScriptScript{ha,MSSo,MSSn}.acceptO

n()mh.send(new Req());mh.moveTo(MSSn);end_step(); // cut Cserver.accept(Req);mh.accept(Res);

ScriptScript{ha,MSSo,MSSn}.acceptO

n()mh.send(new Req());mh.moveTo(MSSn);end_step(); // cut Cserver.accept(Req);mh.accept(Res);

Independent events

MobiCS:MobiCS:Deterministic Simulation Deterministic Simulation

OutputOutput

Programmer may add printout of messages in Programmer may add printout of messages in specific event handlersspecific event handlers

User-configurableUser-configurable Event Log Event Log generated by generated by MobiCS´ simulation engine.MobiCS´ simulation engine.

Exceptions raised during execution of either Exceptions raised during execution of either the script or the protocol code.the script or the protocol code.

MobiCS:MobiCS:Stochastic Simulation Stochastic Simulation

Allows “performance analysis” of a protocol (i.e. message Allows “performance analysis” of a protocol (i.e. message complexity) complexity)

Conists of a continuous test with randomly generated events. Conists of a continuous test with randomly generated events. User creates a User creates a simulation modelsimulation model::

Defines the behavior of all network elements concerning Defines the behavior of all network elements concerning mobilitymobility and and connectivityconnectivity..

Simulation Model can be:Simulation Model can be: programmedprogrammed (extending classes) or (extending classes) or configuredconfigured (instantiation of pre-defined objects). (instantiation of pre-defined objects).

A simulationObject (for each network element) determines A simulationObject (for each network element) determines whether an event of certain type will be generated at each whether an event of certain type will be generated at each simulated time unitsimulated time unit..

Using MobiCSUsing MobiCS

Protocol Implementation Protocol Implementation extend basic extend basic classes classes ProtocolProtocol and and MessageMessage

Implement the Network Elements and Implement the Network Elements and configure the network to be simulated configure the network to be simulated extend basic classes extend basic classes MssMss, , MhMh, ..., ...

Build the simulation scenarios:Build the simulation scenarios:Choose the deterministic scenarios Choose the deterministic scenarios program program

deterministic script deterministic script run simulation run simulation compare compare expected and real resultexpected and real result

Choose stochastic simulation model Choose stochastic simulation model create create corresponding simulation objects corresponding simulation objects run simulations run simulations analyse event log analyse event log

Hand-off

server

proxy

MSSpMh

MSSo

MSSn

ExampleExampleRDP RDP

Req

ReqRes

Greet

DeRegPList

UpCurLoc

ForwardRes

?

Greet

DeReg PList

UpCurLoc

ForwardRes

FRes

Ack

Ack

Ack

Proxy created

RDP Structuring: RDP Structuring: Protocol Interactions Protocol Interactions

wirelesswireless

wiredwired

handoffhandoff

Mss

wirelesswireless

wiredwired

handoffhandoff

Mss

wirelesswireless

Mh

ForwardRes

Ack

RemPListForwardResPList

UpdCurrLoc

DeReg

Req,Ack

ForwardRes

• Protocol structured as 3 micro-protocols wired, wireless e handoff

RDP Structuring:RDP Structuring:Protocols Protocols

Since there are 3 types of network elements, Since there are 3 types of network elements, Server, Mh and Mss Server, Mh and Mss ......

we need to declare following we need to declare following Protocol interfaces: Protocol interfaces:

Define 3 protocol instances (subclasses of Define 3 protocol instances (subclasses of Protocol): Protocol): RDPServer, RDPMh, RDPMssRDPServer, RDPMh, RDPMss,, that that implement the corresponding implement the corresponding ProtocolsProtocols

RDPHandOffModuleRDPMssWiredRDPMssWirelessRDPMhWirelessRDPServerWired

Example:Example:Network Configuration Network Configuration

mh = mh = newnew MyMh( MyMh(“Mh 1"“Mh 1",sim);,sim);cell1 = cell1 = newnew Cell(); Cell();cell2 = cell2 = newnew Cell(); Cell();cell3 = cell3 = newnew Cell(); Cell();mss1 = mss1 = newnew MyMss( MyMss(“Mss 1"“Mss 1",sim,cell1);,sim,cell1);mss2 = mss2 = newnew MyMss( MyMss(“Mss 2"“Mss 2",sim,cell2);,sim,cell2);mss3 = mss3 = newnew MyMss( MyMss("Mss 3""Mss 3",sim,cell3);,sim,cell3);wr = wr = new new WiredLink(mss2.getAddress(),WiredLink(mss2.getAddress(), mss1.getAddress());mss1.getAddress());wr2 = wr2 = newnew WiredLink(mss1.getAddress(), WiredLink(mss1.getAddress(), mss3.getAddress());mss3.getAddress());

mh = mh = newnew MyMh( MyMh(“Mh 1"“Mh 1",sim);,sim);cell1 = cell1 = newnew Cell(); Cell();cell2 = cell2 = newnew Cell(); Cell();cell3 = cell3 = newnew Cell(); Cell();mss1 = mss1 = newnew MyMss( MyMss(“Mss 1"“Mss 1",sim,cell1);,sim,cell1);mss2 = mss2 = newnew MyMss( MyMss(“Mss 2"“Mss 2",sim,cell2);,sim,cell2);mss3 = mss3 = newnew MyMss( MyMss("Mss 3""Mss 3",sim,cell3);,sim,cell3);wr = wr = new new WiredLink(mss2.getAddress(),WiredLink(mss2.getAddress(), mss1.getAddress());mss1.getAddress());wr2 = wr2 = newnew WiredLink(mss1.getAddress(), WiredLink(mss1.getAddress(), mss3.getAddress());mss3.getAddress());

Example: Choosing a Example: Choosing a Deterministic Scenario Deterministic Scenario

Goal: Test protocol when ForwardRes Goal: Test protocol when ForwardRes arrives at a MSS while a Mh is migrating to arrives at a MSS while a Mh is migrating to another cellanother cell

server

proxy

MSSpMh

MSSo

MSSn

?

Greet

DeReg PList

UpCurLoc

ForwardRes

FRes

Ack

Ack

Ack

Req

ReqRes

Greet

DeRegPListUpCurLoc

ForwardRes

Proxy created

MSSo receives ForwardRes beforehandoff of Mh is completed

MSSo receives ForwardRes beforehandoff of Mh is completed

Example: Example: Scripting the Scenario Scripting the Scenario

server

proxy

MSSpMh

MSSo

MSSn

?

Greet

DeReg PList

UpCurLoc

ForwardRes

FRes

Ack

Ack

Ack

Req

ReqRes

Greet

DeRegPListUpCurLoc

ForwardRes

Proxy created

Server.acceptTurnOn(false);MSSn.acceptTurnOn(false);Mh.send(new Req());Mh.moveTo(MSSo);end_step();Mh.moveTo(MSSn);end_step();Server.acceptTurnOn(true);end_step();MSSn.acceptTurnOn(true);

Server.acceptTurnOn(false);MSSn.acceptTurnOn(false);Mh.send(new Req());Mh.moveTo(MSSo);end_step();Mh.moveTo(MSSn);end_step();Server.acceptTurnOn(true);end_step();MSSn.acceptTurnOn(true);

Example:Example:Stochastic Simulation Stochastic Simulation

Example of a Simulation ModelExample of a Simulation ModelMH ActivityMH Activity and and Cell AttractionCell Attraction

Activity: probability that a MH is active (reachable) Cell Atraction: probability that a migrating MH chooses the

cell as its target cell MobilidadeMigration Willingness: probability that a MH moves to another

cell

Network TopologyNetwork Topology: neighbourhood relation among : neighbourhood relation among cellscells

Wireless QoSWireless QoS: Effective wireless transmission rate : Effective wireless transmission rate Application requestsApplication requests: probability that a service is : probability that a service is

requested from the protocol (e.g. RDP request)requested from the protocol (e.g. RDP request)

Stochastic Simulation: Some Stochastic Simulation: Some Results Results We measured how the number of re-transmissions We measured how the number of re-transmissions

(ForwardResult) per Requests is affected by the Mobility Factor (ForwardResult) per Requests is affected by the Mobility Factor Mobility factor = probability that a migration event is generated Mobility factor = probability that a migration event is generated

every n simulated time units every n simulated time units

Other tests: size of proxyList with growing Request/Migration Other tests: size of proxyList with growing Request/Migration RatioRatio

ConclusionConclusion: RDP´s message overhead grows quickly with : RDP´s message overhead grows quickly with increasing migration and request rates. increasing migration and request rates.

0

0.5

1

1.5

2

0 0.2 0.4 0.6 0.8 1

Migration Factor

Forw

ardR

esul

t /

Req

uest

s

ConclusionsConclusions

MobiCSMobiCS Flexible simulation environment that Flexible simulation environment that integrates protocol testing (correctness) and integrates protocol testing (correctness) and performance analysisperformance analysis

Supports modular and extensible prototyping of Supports modular and extensible prototyping of distributed protocols distributed protocols OO and OO and micro-protocolsmicro-protocols

Provides deterministic and stochastic simulation Provides deterministic and stochastic simulation modes, and allows for other modes (e.g. parallel) to modes, and allows for other modes (e.g. parallel) to be programmed.be programmed.

Protocol implementation is totally independent of Protocol implementation is totally independent of

the chosen simulation mode.the chosen simulation mode.

ConclusionsConclusions Main Contributions:Main Contributions:

Implementation of a tool for prototyping and analysis of Implementation of a tool for prototyping and analysis of distributed protocols distributed protocols MobiCSMobiCS

Proof of concept of:Proof of concept of:Reference ArchitectureReference Architecture for flexible and extensible for flexible and extensible

simulators for Mobile Computing.simulators for Mobile Computing.Framework for the implementation of MC simulation Framework for the implementation of MC simulation

models and integration in a simulatormodels and integration in a simulator

Usability Usability MobiCS has been used in a graduate courses at IME/USP MobiCS has been used in a graduate courses at IME/USP

to implement a multicast protocol MCAST [Acharya93]to implement a multicast protocol MCAST [Acharya93]

Conclusions Conclusions

Future Works: Future Works: Define “Network Emulation API” Define “Network Emulation API” MobiCS as a MobiCS as a

testbed for MC applicationstestbed for MC applicationsBuild library of mobility and wireless QoS models.Build library of mobility and wireless QoS models.Implement parallel simulation mode.Implement parallel simulation mode.Create Graphic User Interfaces Create Graphic User Interfaces script creation, script creation,

log-based animation, protocol debugginglog-based animation, protocol debugging

MobiCS is freely availableMobiCS is freely availableURL URL http://www.ime.usp.br/~rcarocha/mobicshttp://www.ime.usp.br/~rcarocha/mobics